Not sure about copy-paste queue logic

So I am not sure how to explain this.

Sometimes when I copy and paste something that takes a while to finish, then I start another copy-paste job while the first one is in progress, the second job is put in a queue. But sometimes if I start a third copy-paste job, it will start a parallell job, and start a new queue. Even when the first queue is not finished.

What I can't figure out is: When does it start a new queue? How do I add all copy-paste jobs to the same queue?

The default copy queue logic is described here: Copy Queues.